Surely you only need one modem, not 2 (like you write you have now) or 3.
If you don't know the difference between a modem, a router, a switch and a WAP, better explain your problem to the sales assistent in the shop where you buy your IT stuff to get what you need including installation instructions.
Hi,
I recently got fibre installed to my house. And in my house i have a fibre modem which is then connected to my wireless modem inside my house. I have a outhouse which gets pretty much no connection. I want to be able to have the full connection out in the outhouse. I have a pipe that runs from were the modem in the house is to the outhouse and it has a LAN cable running through it i was wondering if i could plug the LAN cable to a modem in the outhouse and the other end into the fibre modem. and use that to boost my connection but i am not sure if the two modems will interfere
is this possible if not what can i do?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic